Water and waste water are commonly treated using a variety of conventional techniques. For example, waste water can be treated by aerobic, anoxic, and/or anaerobic processes, depending upon the characteristics of the waste water and the intended result of the treatment. Each of these processes requires different types of bacteria and utilizes a different mechanism for removing contaminants. Consequently, it is desirable for a treatment system to be flexible such that it can effect anaerobic, anoxic or an aerobic environment, either at different times or in different parts of the treatment system at the same time, or by controlling system variables.
In activated sludge systems, the microbial organisms are free floating and are circulated in the basin or other treatment reactor so that they contact the soluble and particulate contaminants in the liquid. In other systems the microorganisms are fixed in place and the contaminants are circulated to them. In either case, the soluble waste and small particulate waste are the materials that are the primary focus of treatment and are most difficult to remove from the liquid.
Submerged media of various types have been used to provide a base for accumulating and growing microbial biomass in treatment basins. Rigid parallel plates and honeycomb structures allow the liquid to pass between them and contact the biomass that accumulates on the plate and the honeycomb cells. However, the rigidity of these structures allows essentially unlimited buildup of biomass, so they must be cleaned frequently or they clog unduly and disrupt the treatment operation when used as submerged media in a high organic loading or in a low water flow environment. The need for frequently cleaning results in significant maintenance costs and other problems such as down time of the treatment facility which limits the application of rigid systems of this type.
Other types of media have been proposed, including unusual media elements confined in a cage structure through which the liquid passes. Although media of this type function in a satisfactory manner in many respects, there are significant problems. Again, excessive biomass builds up on the media and must be removed frequently to prevent clogging. Further, the liquid must be pumped through the media using relatively complex and costly pumping systems. The media is costly and typically involves the use of baffles and other flow control devices to achieve the necessary flow pattern. Distributing the caged media properly throughout the reactor also presents problems. All of these factors detract from the viability of caged media systems for use in many applications.
Woven net structures have been used involving strands or other elements strung between support members in the reactor. These systems are disadvantaged in that they are costly, difficult to properly distribute throughout the basin, have inadequate surface to volume ratios, and have elements that are fixed at both ends and thus relatively inflexible so that excess biomass can accumulate and clog the media.
The foregoing systems were developed for use as packing in towers or for trickling filter applications where the liquid flows vertically across media surfaces and has a velocity sufficient to shear off excess biomass. However, when they are submerged in much lower velocity basins or lagoons with relatively slow horizontal flow and significant organic loading, the velocity is inadequate for biomass removal. Thus, the cleaning and maintenance requirements previously identified are inherent. The process control parameters in a basin or lagoon also differ markedly compared to a trickling filter, and there is a need to distribute the media horizontally and vertically in a very large reactor which is not present in a small volume trickling filter application.
U.S. Pat. Nos. 6,060,153; 6,171,686; 6,230,654 and 6,244,218 to McNeil disclose woven fabric in the form of thin sheets used primarily in aquaculture environments. The sheets may be split in their lower portions to form side by side strips. However, each strip is a thin planar structure having a thickness of only about ⅛ inch or less. The water can pass through the slits, but each strip is essentially two dimensional so that the liquid flows quickly past the media and at most contacts only one strip. The strips are flexible fabric and film surfaces which stick together when placed close to each other. There is no three dimensional flow through effect and no baffling effect that directs the liquid from one media element to another. Therefore, contact between the particles in the liquid and the biomass on the media is not effected in an optimal manner.
Aquacultural systems have need for waste removal as well as other needs. For example, fish and other aquatic life must be protected against ammonia contamination. The ammonia that makes its way into the water must be converted to nitrate in a nitrification process involving one type of biogrowth, and the nitrate may then be converted to nitrogen gas in a de-nitrification (removal) process involving different types of microbes. Additionally, an environment can be provided where small fish and hatchlings are protected from predators, and the fish can utilize much of the biogrowth such as snails and other lower level organisms to feed on. Proper application of submerged media allows soil or floor erosion to be stabilized where it has been allowed to occur. The aquacultural systems proposed in the past have not adequately addressed all of these concerns.